The present invention relates to a method and an apparatus for tunnelling.
The conventional method for tunnelling entails the use of a "shield mill" which bores the entire cross-section of the tunnel, the final supporting structure of the tunnel being produced behind said mill.
This method has limitations due to the need to have a shield which has exactly the dimensions of the tunnel to be bored and cannot therefore be used in tunnels with different geometry.
Considerable excavation power is furthermore required. Another disadvantage is to be seen in the fact that in loose soil a downward thrust component is induced which is due to the weight of the excavation tool and is difficult to control.